Do I need insulation under my house?

I have a 2 story home that has a basement with a dirt floor. I don't know if I should insulate the main level floors, could this cause mold to grow?

Benny ~ Catlettsbug, KY

Hi Benny. Anytime moisture gets into an enclosed space and is allowed to remain, there is a chance mold will grow. Adding insulation to the floors shouldn't do anything to increase or decrease the likelihood of mold in your basement -- the big issue is whether you already have dampness or standing water in that area.

Basements that are entirely below grade are notorious for moisture problems anyway and having a dirt floor only compounds the problem. I know from experience as that is exactly the situation I have in a portion of the basement of my old house. Pouring concrete on the floor would help, but unfortunately most of these types of basements don't allow much accessibility from the exterior so using a chute or even a wheelbarrow is often out of the question. If you're not getting any standing water in the space after a rain and don't plan to ever do any basement finishing, you might be able get by with just a dehumidifier down there.

Once you feel you have the moisture in the space under control, insulation can be installed between the floor joists. I would install a layer of poly vinyl on the bottom of the joists after the insulation is in place to act as a vapor barrier. Overlap the joints in the plastic about a foot if possible.

If you have vents in your basement, opening them during the spring and fall will allow air to circulate and help prevent moisture buildup. However, the vents should be closed during the summer to prevent humid air from entering and during the winter to keep cold air out of your home.